Electric heating – Metal heating – By arc
Patent
1992-01-14
1994-03-22
Albritton, C. L.
Electric heating
Metal heating
By arc
21912175, B23K 2618
Patent
active
052966739
DESCRIPTION:
BRIEF SUMMARY
This invention relates to apparatus and methods for laser ablation machining by projection imaging using an excimer laser.
Such projection imaging is known, for example from U.S Pat. No. 4508749, which describes excimer laser ablation etching of thin (5 micrometer) polyimide layers on microelectronic integrated circuit devices. The ultraviolet light from an excimer laser passes through a mask into a telecentric lens system which projects a reduced size image of the mask onto the 5 micrometer target layer of polyimide, thereby photoetching openings corresponding to the mask pattern in the polymide layer with a 55.degree. to 60.degree. slope on the sidewalls of the openings.
The present invention provides a system which is particularly well suited to producing through-holes in thicker polymer films, preferably self-supporting films, as described for example in EP-A-0213774 or in co-pending International Applications PCT/GB89/00110, PCT/GB89/00111, PCT/GB89/00108, and PCT/GB89/00109. Other uses of the system according to the present invention can be envisaged and are not excluded.
One aspect of the present invention provides an apparatus for excimer laser image projection ablation of a target material comprising a projection lens system for projecting a mask pattern to be ablated onto the target, which lens system is telecentric towards the image (target) end of the projection path, and means for moving the target along the protection path whereby in use the size of the projected image areas to be ablated from the target is adjusted substantially without altering their relative positions on the target. The de-magnification remains substantially unchanged, due to the telecentricity of the lens system, and the slightly diffuse focus on moving the target away from the true image plane leads to larger images of the mask apertures being formed, surprisingly without unacceptable loss of definition in the ablated pattern. It has been found, for example, that the target can be moved tens or even hundreds of micrometers away from the nominal focal plane of a telecentric lens whilst maintaining accurate centre-to-centre spacing and acceptable resolution of ablated features. Resolution of, for example, less than or equal to 2 micrometers can be achieved, and this is assisted by the non-linearity of ablation depth in proportion to applied fluence, which tends to suppress ablation in diffuse image areas where the fluence falls below the threshold for ablation.
Preferably the multi-elements lens system is telecentric only on the image (target) side, so that movement of the mask object along the optical axis can be used to alter the de-magnification slightly, for example within a range from 4.9:1 to 5.1:1, thus slightly altering the aperture spacing in the image to fit various end use requirements. In this way, for example, patterns may be machined in polymer films with dimensions "tailored" to allow for thermal expansion, without the need to fabricate a new mask. By combining both the mask and target adjustment great versatility can be achieved.
In another aspect of the invention, to cover larger areas, the projected image may be "stepped and repeated" across the target by mounting the target on a moveable stage (provided the image has a repeat pattern), or the beam may be scanned, preferably by deflection using a mirror which is moved linearly to translate the laser beam across the surface of a mask which is larger in area than the beam emanating from the excimer laser. Alternatively, the mirror could be rotated slightly to scan the beam through a small angle, or a triangular acute-angled quartz prism could be rotated to scan the beam passing through it by altering the refraction angles. Scanning of the beam in that one of its directions which has an approximately Gaussian intensity distribution tends to homogenise the beam with advantageous results in uniformity of ablation. The beam can be scanned in two dimensions by combining (for example) a scanning mirror and a prism.
Another aspect of the invention is that the shap
REFERENCES:
patent: 4508749 (1985-04-01), Brannon et al.
patent: 4780177 (1988-10-01), Wojnarowski et al.
patent: 4801068 (1989-03-01), Shimazu et al.
patent: 4907341 (1990-03-01), Chapel, Jr., et al.
patent: 5095190 (1992-03-01), Aketagawa et al.
Albritton C. L.
Burkard Herbert G.
Raychem Limited
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